The present invention relates to an air conditioning system using a refrigerant to control a temperature of a climate-controlled area. More specifically, the present invention relates to an air conditioning system utilizing a compressor driven by an electric motor and having an adjustable compression mechanism to control a current pressure in the refrigerant circuit thereby controlling the temperature of the climate-controlled area.
Air conditioning systems using a refrigerant are well known in the art for controlling a temperature of climate-controlled areas such as interiors of buildings, vehicle cabins, meat lockers, and the like. A typical prior art, air conditioning system for controlling the temperature of the climate-controlled area comprises a refrigerant circuit for circulating the refrigerant under a pressure. A compressor compresses the refrigerant in the refrigerant circuit and forces the refrigerant in the form of a pressurized gas to a condenser. The condenser then condenses the pressurized gas refrigerant into a pressurized liquid refrigerant. From there, the liquid refrigerant is conveyed to an expansion device in which the liquid refrigerant is expanded to reduce pressure and temperature. Next, the refrigerant is conveyed to an evaporator. Air to be cooled travels across the evaporator and the refrigerant inside the evaporator absorbs heat from the air thereby boiling the refrigerant and converting the refrigerant into a gas. Once the refrigerant has been cycled through the evaporator, an accumulator-dehydrator may be used to separate any remaining liquid refrigerant in the refrigerant circuit that has passed through the evaporator. Liquid refrigerant may foul the compressor. Finally, once separated, the gas refrigerant is conveyed back to the compressor to begin the cycle again.
Typically, when the climate-controlled area is a vehicle cabin, the compressor is belt-driven by a motor of the vehicle. However, more recently, as a result of the trend toward electric, hybrid, and fuel cell vehicles, the compressor is electrically operated. Electrically operated compressors are generally more efficient and in these types of vehicles, energy conservation via efficient components is critical. Likewise, when the climate-controlled area is a building or a meat locker, the compressor is typically electrically operated. Such systems generally utilize variable speed electric motors to adjust a current pressure in the refrigerant circuit to control the temperature of the climate-controlled area. The ability to vary the current pressure in the refrigerant circuit is important in maximizing efficiency of the compressor under different cooling conditions. While variable speed electric motors are capable of varying the current pressure of the refrigerant circuit, most electric motors have a maximum efficiency at one particular speed. Hence, varying the speed of the electric motor is counterproductive in maximizing efficiency of the compressor under different cooling conditions. Furthermore, the electronics required to operate the electric motor at variable speeds are costly, complex, and unreliable.
In alternative systems, multiple compressors operating at different speeds to generate different compression rates are utilized and the air conditioning system varies engagement of these compressors based on different cooling conditions to maximize efficiency. However, such systems are costly and require complex electronics to switch between the compressors.
One solution to the aforementioned problems is suggested in U.S. Pat. No. 6,230,507 to Ban et al. The ""507 patent to Ban et al. shows an air conditioning system utilizing a compressor in a refrigerant circuit for controlling a temperature of a climate-controlled area. The compressor of Ban et al. utilizes a variable speed electric motor for driving the compressor. In addition, an adjustable compression mechanism for compressing the refrigerant is also utilized. Ban et al. teaches adjusting the compression mechanism, as well as adjusting the speed of the electric motor to maximize efficiency of the compressor. In Ban et al., the compression mechanism includes a swash plate and a plurality of pistons engaging the swash plate, as is well known in the art. An electronic control valve is used to vary an inclination angle of the swash plate thereby adjusting the compression mechanism and changing a current pressure in the refrigerant circuit.
Still referring to Ban et al., a controller controls the electronic control valve based on a cooling load on the refrigerant circuit. For example, when the cooling load is great, the controller controls the electronic control valve to reduce the pressure in a crankcase chamber in which the compression mechanism is located thereby increasing the inclination angle of the swash plate. This increases the compression or displacement of the compressor. The controller calculates the cooling load based on an evaporator temperature, a desired or target temperature for the climate controlled area, the current temperature of the climate-controlled area, and an outside temperature. This information is sent to the controller via control signals from sensors in the air conditioning system.
The present invention provides an air conditioning system using a refrigerant to control a temperature of a climate-controlled area. The air conditioning system comprises a refrigerant circuit for conveying the refrigerant at a pressure. A compressor housing is coupled to the refrigerant circuit and a compression mechanism is disposed in the compressor housing to compress the refrigerant. An adjustment mechanism adjusts the compression mechanism between a plurality of stroke positions to adjust a current pressure in the refrigerant circuit. A motor having a drive shaft coupled to the compression mechanism is electrically operated to move the drive shaft. A controller is programmed to determine a target pressure for the refrigerant circuit and to control the adjustment mechanism to adjust the compression mechanism between the plurality of stroke positions. This adjusts the current pressure in the refrigerant circuit. A pressure sensor is coupled to the refrigerant circuit to measure the current pressure in the refrigerant circuit and transmit a signal to the controller indicative of the current pressure. The controller then controls the adjustment mechanism to adjust the current pressure in the refrigerant circuit until the current pressure is within a predetermined pressure limit of the target pressure.
A method of controlling the temperature of the climate-controlled area using the air conditioning system is also provided. The method comprises the steps of measuring a current temperature of the climate-controlled area and establishing a target temperature for the climate-controlled area. Next, a temperature difference between the measured current temperature and the established target temperature is determined. A target pressure is then selected based on the determined temperature difference. A current pressure in the refrigerant circuit is measured and a pressure difference is determined between the selected target pressure and the measured current pressure. The pressure difference is then compared to a predetermined pressure limit. When the pressure difference exceeds the predetermined pressure limit, the current pressure in the refrigerant circuit is adjusted until the determined pressure difference is within the predetermined pressure limit.
The present invention provides several advantages over the prior art. For example, the pressure sensor permits the system to accurately measure a current pressure in the refrigerant circuit. Furthermore, adjusting the compression mechanism between the plurality of stroke positions to adjust the current pressure, while measuring the current pressure, results in a more responsive air conditioning system than systems that adjust the compression mechanism based on temperature of an evaporator. In other words, the adjustment of the compression mechanism can be more precisely controlled and the compressor is more responsive to changing conditions than with prior art systems.